1. Field of Invention
The invention relates to an apparatus for the treatment of a medical liquid. The apparatus includes a treatment machine having a coupling surface and a flexible mat arranged on the coupling surface, and a cassette made from a hard material, the cassette including liquid conducting passages which are covered by a flexible film that is couplable to the coupling surface of the treatment machine via the flexible mat. The apparatus also includes suction openings in the cassette that facilitate a removal via suction of air from between the flexible film and the flexible mat, and an element that determines deflection of the flexible mat or of parts of the flexible mat. The invention furthermore relates to a method for checking the leak tightness of the aforesaid apparatus.
2. Description of the Prior Art
A corresponding apparatus for the treatment of a medical liquid can, by way of example, be a blood treatment machine such as is used in hemodialysis or in peritoneal dialysis. In such a use, the medical cassette includes the blood-conducting or dialysis liquid-conducting passages and is in communication with actuators and sensors of the treatment machine via the coupling surface. The medical cassette can thus be configured as a cost-effective disposable part, whereas the actuators for the control of the liquid flow through the cassette and the sensors are integrated into the treatment machine for the level detection or for the pressure measurement.
Such medical cassettes configured as disposable articles comprise in this connection a thin-walled three-dimensional hard plastic part having a planar peripheral contact edge and various recesses (chambers, webs and passages). Medical liquids such as dialysate or blood can now be conducted in the chambers and passages formed by these three-dimensional structures of the hard plastic part. The contact plane of the cassette is closed in a liquid tight manner by a flexible film, advantageously a polymer film which is peripherally connected, in particular welded and/or adhesively bonded, to the contact edge of the hard part. The medical cassette is pressed onto the coupling surface of the treatment machine in use with the flexible film so that actuators and sensors of the treatment machine lie on the polymer film. In addition, the flexible film is pressed together with the webs of the cassette by this pressing and thus provides a fluid tight separation of the liquid-conducting passages in the hard part by the webs and the flexible film.
Furthermore, the cassette passages can also be welded or adhesively bonded to the flexible film to achieve a fluid-tight separation of the liquid-conducting passages.
The coupling surface of the treatment machine accordingly usually has actuators, sensors and pressing force transmission surfaces. The actuators and sensors of the blood treatment machine are arranged in this context in the coupled state of the cassette opposite the liquid-conducting passages of the cassette. The actuators can hereby form valves by the pressing down of the film in that the flexible film is pressed into regions of the liquid-conducting passages and closes them. The sensors, for example, measure the pressure or temperature of the liquid located in the liquid-conducting passages. In an embodiment of the cassette, the pressing force transmission surfaces can press the flexible film against sealing webs of the hard part which surround the liquid-conducting passages to seal them with respect to one another and with respect to the rest of the cassette. Alternatively, the cassette passages can also be welded or adhesively bonded. The coupling surface is usually formed by a planar surface of a support member which is made e.g. from metal, with receivers for the sensors and the actuators being provided in said surface, and by the sensors inserted into these receivers in planar fashion.
A flexible mat, made, for example, of silicone or another elastomeric material, is usually arranged on the coupling surface of the treatment machine. This has the advantage that the sensor surfaces are protected against environmental influences and the machine surface is moreover liquid tight and thus ideally hygienically cleanable. The flexible mat in this context represents a part of the treatment machine to which the cassette is coupled as a disposable part. The operation of the actuators is ensured by the flexibility of the mat. In addition, the flexible film can be pressed well to the coupling surface via the flexible mat, whereby a good contact with the actuators, sensors and pressing force transmission surfaces is made possible.
On the coupling of the sensors to the film surface, there is the difficulty with known surfaces of achieving a good coupling to obtain correct measured values. In particular air which is trapped in the transmission path between the flexible film and the sensor surface on the insertion of the cassettes produces a falsification of the measured results. This applies to pressure sensors (in particular on the measurement of pressures which are less than the environmental pressure), but also in level detection and likewise to actuators such as valves. Unwanted air enclosures between the outer surface of the flexible film and the mat surface of the flexible mat lying thereon should therefore be eliminated on the coupling. This usually takes place by air suction.
It is already known from DE 101 57 924 C1 and DE 102 24 750 A1 to realize the air transport by means of integrated mat passages, predetermined in a defined manner, on the rear side of the machine mat at the machine side. The air line from the surface of the flexible film through the mat to the air passages arranged on the machine side takes place locally through uninterrupted slots in the region of the mat passages. The air transport however, hereby only takes place at precisely defined points of the flexible film of the cassette at which the air is sucked off through the slots in the mat to the mat passages arranged on the machine side. These mat passages therefore have to be located in the region of the liquid-conducting passages of the cassette to ensure a good suction there, which can lead to safety problems. In this embodiment, the sensor surface is no longer ideally protected from environmental influences and is not necessarily hermetically sealed by the mat so that hygienic problems can, for example, occur.
To improve the reliable air suction and for the reliable prevention of air islands, an apparatus for the treatment of a medical liquid is proposed in DE 10 2007 042 964 A1 in which a layer of an air-permeable porous material is arranged between the flexile film and the coupling surface in the coupled state, with air being able to be sucked out areally through said layer during the coupling process and/or with a coupled cassette.
To satisfy the hygienic demands, it is necessary to manufacture a closed, liquid-tight surface without sealing points, joints or material transitions. The previously mentioned uninterrupted flexible mat, which is made of silicone rubber, serves exactly this purpose. It separates the sensors and actuators from the cassette film. Two regions which have to be evacuated for the coupling of the cassette result on the basis of this separation, namely the region between the mat and the coupling surface and, on the other hand, the region between the upper side of the mat and the cassette film. Whereas the suction at the machine side between the coupling surface and the mat side facing it is solved for the sufficiently provided air conduction passages in the aforesaid DE 10 2007 042 964 A, the coupling on the cassette side is more complex and/or expensive on the cassette side due to the high demands on the cleanability and due to the machine surface.
If, for example, an intermediate space should arise between the flexible mat and the cassette film due to air leakages from the outside, this can result in the decoupling of the actuators and in incorrect measurements of the sensors.
The reasons for a collapse of the vacuum between the flexible mat and the film of the cassette lying thereon can be insufficient sealing to the ambient air. A good air permeability between the silicone mat and the film is required on the suction of the cassette film. However, it must be interrupted in the marginal region of the cassette.
A high demand is thereby made on the sealing tightness between the film and the flexible mat so that comparatively high pressure differences can be maintained. If leaks occur due to dirt, damage, collapsed points or foreign bodies, the vacuum cannot be maintained.
In known apparatus, a suction opening with a hydrophobic membrane is provided for the suction of any air present between the film and the flexible mat. The known systems are, however, very prone to failures, with corresponding failures here not being able to be detected with known apparatus. If, for example, a closure of the hydrophobic membrane of the aforesaid suction opening arises due to liquid, it cannot be detected by the machine whether the intermediate space between the film and the flexible membrane was actually evacuated. The suction can likewise be realized by an opening in the mat 12. Leak detectors on the machine side can thereby also recognize a liquid leak when a protective device with a hydrophobic membrane is provided.
If, on the other hand, due to a kinking of the pneumatic hoses in the machine, a closure of the hose occurs, the suction process of the air from the intermediate space between the film ad the flexible mat is interrupted.
A particularly critical case which can occur in an extreme case consists of the fact that on damage to the film, blood, for example, emerges from the cassette and fills the intermediate space between the film and the flexible mat. It is here not just a question of ensuring the coupling of the sensors and actuators to the cassette, but rather also to avoid the blood loss and a potential contamination of the patient's blood.
Generally, sufficiently good suction can be ensured by the evacuation possibilities between the film and the flexible mat. In this respect, not only the suction of air is possible, but rather also that of liquids—such as blood. It can thereby be assumed on a liquid leak, precisely as with a gas leak, that the penetrating medium is conveyed up to the suction opening.